Multi-layered implant

ABSTRACT

A multi-layered implant and methods of forming the multi-layered implant are disclosed. The multi-layered implant includes a Metal Injection Molded body comprising a titanium alloy, a porous coating layer on a first surface of the Metal Injection Molded body, and a zirconium alloy layer on a second surface of the Metal Injection Molded body. The first surface and the second surface are on opposite sides of the Metal Injection Molded body. A zirconia layer may be formed over the zirconium alloy layer. The porous coating may be a titanium-based porous coating.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 15/195,624, filed Jun. 28, 2016, and published as U.S. Patent App. Pub. No. 2016/0305005 on Oct. 20, 2016, which is a continuation-in-part of U.S. patent application Ser. No. 14/061,466, filed Oct. 23, 2013, and issued as U.S. Pat. No. 9,404,173 on Aug. 2, 2016, the disclosures of which are hereby incorporated by reference herein.

TECHNICAL FIELD

The present application generally relates to a multi-layered implant. In particular, the present application relates to an implant including a titanium substrate layer, a zirconia layer, and a titanium-based porous layer, and methods for forming such an implant.

BACKGROUND

Known methods for producing metal bodies for medical implants are not satisfactory for the range of applications for which they are employed. For example, cobalt chrome alloy implants are useful for high strength applications. Nevertheless, known cobalt chrome alloy implants include nickel, which can cause undesirable patient interactions for individuals having nickel sensitivities and/or allergies. Further, known cobalt chrome alloy implants are typically heavier than alternative implants, which may lead to long term discomfort and/or complications when implanted in a patient.

Titanium alloy implants provide an alternative nickel-free implant for sensitive/allergic patients. Known titanium alloy implants are useful, for example, for applications requiring lower material strength. Titanium alloy implants may also be useful where typical casting processes for many implants are not required. For example, titanium alloy implants can be machined. However, titanium alloy implants are expensive to machine in implant geometries.

Zirconium alloy implants having a zirconia surface demonstrate improved wear performance over cobalt chrome and also provide a nickel-free alternative for patients with nickel sensitivities/allegories. Nevertheless, known zirconium alloy implants cannot be used with cement-less interface applications unless plasma sprayed and thus fail to capitalize on the improved fixation durations and avoidance of negative patient interactions provided by cementless interface applications.

Accordingly, there exists a need for implants that address the above deficiencies and methods for manufacturing such implants.

SUMMARY

Aspects of the present disclose are directed to a multi-layered implant. Methods of forming a multi-layered implant are also disclosed. In some embodiments, the multi-layered implant includes a Metal Injection Molded body including a titanium alloy. The multi-layered implant also includes a porous coating layer on a first surface of the Metal Injection Molded body. The multi-layered implant also includes a zirconium alloy layer on a second surface of the Metal Injection Molded body. The first surface and the second surface may be on opposite sides of the Metal Injection Molded body.

In some embodiments, the porous coating layer may include a titanium-based porous coating. The multi-layered implant may also include a zirconia layer over the zirconium alloy layer. The zirconium alloy layer may include a zirconium-niobium alloy. The multi-layered implant may be a knee implant, a shoulder implant, an ankle implant, a spine implant, a disc implant, or a hip implant.

In some embodiments, a knee implant includes a titanium alloy substrate, a porous coating layer on a first surface of the titanium alloy substrate, a zirconium alloy layer on a second surface of the titanium alloy substrate, and a zirconia layer over the zirconium alloy layer. The first surface and the second surface may be on opposite sides of the titanium alloy substrate.

In some embodiments, the porous coating layer may include a titanium-based porous coating. The zirconium alloy layer may include a zirconium-niobium alloy.

In some embodiments, a method of manufacturing a multi-layered implant includes providing a metal injection molded body that may include a titanium alloy, applying a porous coating on a first surface of the metal injection molded body to form a porous coating layer, applying a zirconium alloy on a second surface of the metal injection molded body to form a zirconium alloy layer, and oxidizing the zirconium alloy layer to form a zirconia layer over the zirconium alloy layer. The first surface and the second surface may be on opposite sides of the Metal Injection Molded body.

In some embodiments, the Metal Injection Molded body may be provided by receiving the Metal Injection Molded body and/or by molding the Metal Injection Molded body. The zirconium alloy may be applied on the second surface of the Metal Injection Molded body by over-molding the zirconium alloy on the second surface of the Metal Injection Molded body to form the zirconium alloy layer. The Metal Injection Molded body may further be sintered and hot isostatic pressed. Sintering can include the porous coating on the first surface of the Metal Injection Molded body and sintering the zirconium alloy on the second surface of the Metal Injection Molded body.

In some embodiments, the zirconium alloy layer may be polished by, for example, applying an abrasive finishing process to the zirconium alloy layer. The zirconium alloy layer may also be heat treated, and/or the zirconia layer may be mechanically finished. The zirconium alloy layer may be oxidized by heating the zirconium alloy layer in an oxidative environment to form the zirconia layer. The zirconium alloy may include a zirconium-niobium alloy.

Various additional features and advantages will become apparent to those of ordinary skill in the art upon review of the following detailed description of the illustrative embodiments taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description is better understood when read in conjunction with the appended drawings. For the purposes of illustration, examples are shown in the drawings; however, the subject matter is not limited to the specific elements and instrumentalities disclosed. In the drawings:

FIG. 1 illustrates an exemplary process for forming a multi-layered implant;

FIG. 2 illustrates a prospective view of a multi-layered implant implanted into a knee of a patient; and

FIG. 3 illustrates a cross-sectional view of the multi-layered implant depicted in FIG. 2.

DETAILED DESCRIPTION

A multi-layered implant that addresses the shortcomings of conventional implants is described below. For example, the multi-layer implant is nickel free to avoid material sensitivity and allergy issues relative to cobalt chrome alloy implants and is lighter relative to cobalt chrome alloy implants. The multi-layered implant can be produced via a Metal Injection Molded (MIM) process for better technical feasibility relative to cast implants, for better economic feasibility relative to machined implants, and to enable a combination of a titanium alloy body with zirconium alloy that was not previously feasible.

The multi-layered implant also includes a cement-less, porous coating for better bone in-growth and fixation relative to cemented implants. In addition, the multi-layered implant can include a zirconia articular surface for improved wear performance relative to cobalt chrome alloy implants. That is, the multi-layer implant combines materials and surfaces using technically and economically feasible manufacturing processes to provide separate benefits of different materials in a single implant.

The multi-layer implant can include a Metal Injection Molded body having a first layer including a titanium alloy substrate. A zirconium alloy is over-molded onto a first surface of the titanium alloy substrate to form a second layer. The zirconium alloy is oxidized to form a third zirconia layer. A porous titanium-based coating is applied on a second surface of the titanium alloy substrate to form a fourth layer. The first surface and the second surface may be on opposite sides of the Metal Injection Molded body. Although the first, second, third, and fourth layers have been described above, the numerical reference to each layer is for identification purposes only and does not limit the order of the layers of the multi-layer implant. For example, the Metal Injection Molded body could be a core, with the porous titanium-based coating as a second layer, the zirconium alloy as a third layer, and the zirconia as a fourth layer.

Referring to FIG. 1, a flow diagram depicting a method 100 of forming a multi-layered implant, such as the multi-layer implant 200 illustrated in FIGS. 2 and 3, is illustrated. The multi-layer implant 200 can include three, four, or more layers. At step 102, a Metal Injection Molding (“MIM”) body 205 including a titanium alloy is provided. For example, the titanium alloy may comprise commercially pure titanium, a Ti-6Al-4V alloy, a Ti-6Al-4V ELI alloy, a Ti-a3Nb-13Zr alloy, a Ti-12Mo-6Zr-2Fe alloy, a Ti-15Mo alloy, a Ti-3Al-2.5V alloy, and/or a Ti-6Al-7Nb alloy, among others. The titanium alloy MIM body 205 provides a viable alternative implant for patients with nickel sensitivities and/or allergies.

The MIM body 205 may be provided by molding the MIM body 205, storing an already molded MIM body 205, or receiving the MIM body 205 in already molded form from another source, such as a third-party manufacturer. The MIM body 205 may be the first layer, or substrate or core, of the multi-layered implant 200. Molding the MIM body 205 may include mixing a feedstock comprising one or more metal powders and one or more binders.

At step 104, a porous coating is applied to one surface of the MIM body 205. The one surface may be an implant-to-bone surface of the multi-layer implant 200, which attaches to a bone of a patient. The porous coating may be a titanium-based coating, such as a titanium bead coating, an asymmetric titanium particle coating, or a porogen-produced titanium coating. The porous coating may define another layer over the MIM body 205, such as a second or fourth layer of the multi-layered implant 200. The porous coating may have an average pore size between 100 and 500 μm for optimal bone in-growth.

At step 106, a zirconium alloy is applied onto another surface of the of the MIM body 205. In some embodiments, the zirconium alloy may be over-molded onto the other surface of the MIM body 205. The other surface may be an implant-to-implant surface of the multi-layer implant 200, which contacts another implant in the patient. The implant-to-implant surface may be on the side opposite the implant-to-bone surface of the multi-layer implant 200. The zirconium alloy may define another layer, such as a second or third layer of the multi-layered implant 200. In some embodiments, to over-mold the zirconium alloy, the MIM body 205 may be placed in a second mold that is different from the mold used to mold the MIM body 205. A second feedstock including one or more metal powders and one or more binders are mixed together. The second feedstock may then be injected into the second mold, thereby forming an over-molded layer made up of the second feedstock including zirconia alloy over the MIM body 205. The zirconium alloys can be, for example, zirconium-niobium alloy, such as zirconium-2.5 niobium, among others. Zirconium alloys are particularly well suited to oxidation layer formation processes. The over-molded part may contain binders at the conclusion of over-mold processing, which may require removal.

At step 108, the multi-layer implant 200 may be sintered. The resultant sintered porous coating may allow for cement-less applications, which as compared to cemented implants, offer better long-term implant-bone fixation and avoid negative patient interactions that can result for patients with cement sensitivities and/or allergies. The sintering step 108 will fuse the titanium alloy MIM body 205 with the zirconium alloy layer 215. The sintering step 108 may occur after the step 106 of applying the zirconium alloy and before or after the application of the step 104 of applying the porous coating.

In some embodiments, the sintering step 108 can include multiple sintering steps. For example, a first sintering step can follow the step 106 of applying the zirconium alloy to fuse the titanium alloy MIM body 205 with the zirconium alloy layer 215. A second sintering step can follow step 104 of applying the porous coating to improve the connection of the porous titanium-based coating layer 210 to the titanium alloy MIM body 205. The two sintering steps may be performed at the same or similar temperatures for the same or similar time duration, at the same or similar temperatures for different time durations, at different temperatures for the same or similar time duration, or at different temperatures for different time durations. For example, the first and second sintering steps can be performed at similar temperatures for different time durations. In such an example, the zirconium alloy on the MIM body 205 can be sintered for a shorter time duration than the porous coating on the MIM body 205.

At step 110, the multi-layer implant 200 may be hot isostatic pressed. The hot isostatic pressing step 110 may occur before or after the step 104 of applying the porous coating. The multi-layer implant 200 can be placed in a chamber surrounded by an inert fluid, which can be an inert gas, such as nitrogen, argon, helium, neon, argon, krypton, xenon, and/or radon. The inert gas applies a substantially even, predetermined pressure around the entire exposed surface of the multi-layer implant 200 being pressed. Applying pressure evenly effectively reduces the internal porosity of the multi-layer implant 200, thereby improving the mechanical properties such as hardness, smoothness, and uniformity, while retaining a substantially similar shape. Improving the mechanical properties may also partially result from increasing the density of the multi-layer implant 200. Relative to an implant that is not hot isostatic pressed, the higher density multi-layer implant 200 has a reduced porosity and increased material integrity. The pressure applied may be adjusted by introducing or removing inert fluid to or from the chamber or by adjusting the temperature of the contained fluid. In some examples, the multi-layer implant 200 can be hot isostatic pressed at a pressure between 15,000 to 30,000 pounds per square inch (psi) and at a temperature range of 1500 to 2500 degrees Fahrenheit.

At step 112, the multi-layer implant 200 can be processed. The processing can include one or more of a plurality of different processing techniques described below. For example, processing the zirconium alloy layer 215 may improve the surface characteristics, such as grain size and smoothness, and improve acceptance of a zirconia layer at step 114. The processing step 112 may result in layers of the multi-layer implant 200 being more dense, smooth, and uniform.

The processing step 112 may include thermally treating the multi-layer implant 200 by heating the multi-layer implant 200 to a temperature between 1,500 to 2,500 degrees Fahrenheit. Thermally treating the multi-layer implant 200 in this manner may produce, amongst other benefits, finer, more uniform grain boundaries proximate the surface of the multi-layer implant 200 and, in some cases, throughout the multi-layer implant 200. The thermal treatment may, for example, encourage alloy elements and segregated elements at grain boundaries to diffuse within the MIM body 205 and evenly redistribute throughout the internal material. As a result, thermal treating the multi-layer implant 200 may improve mechanical properties, such as toughness and ductility.

In some examples, thermally treating the multi-layer implant 200 may also include a rapid quench step. Specifically, the multi-layer implant 200 may be rapidly quenched at pressure within a lower-temperature quenching fluid to rapidly reduce the temperature of the multi-layer implant 200. The multi-layer implant 200 may, for example, be reduced within a short period of time in a quenching fluid that is 150 degrees Fahrenheit or less. Rapid quenching has been observed to more quickly reduce atomic movement within the multi-layer implant 200 thereby reducing the amount of time required to reset the multi-layer implant 200's microstructure to result in finer, more uniform grain boundaries compared to ambient cooling.

The processing step 112 may also include machining the multi-layer implant 200 to conform the multi-layer implant 200 to precise desired dimensions and to correct any introduced flaws in the processing of the multi-layer implant 200.

The processing step 112 may also include a single state or a multistage abrasive finishing process to encourage the zirconium alloy layer 215 accept a zirconia layer at step 114. For example, the multi-layer implant 200 may be tumbled via particle media that is increasingly fine at each stage. In some embodiments, the abrasive finishing process may include a first polishing step, second polishing step, and a step of protecting an outer surface of the zirconium alloy layer 215.

The processing step 112 may also include peening the zirconium alloy layer 215 by, for example, blasting beads toward the zirconium alloy layer 215. The beads may be spherical glass bead, steel beads, ceramic beads, steel shot, or a combination thereof. The zirconium alloy layer 215 may be peened to alter and refine the zirconium alloy layer 215 surface microstructure as a result of the compressive force applied by the peening media. For example, prior to peening, the surface may define visible exterior grain boundaries, which may reduce the surface's ability to accept a satisfactory oxide layer. Following peening, the visual and structural uniformities of the surface microstructure may be of equal or greater quality than a forged surface. This plastic deformation of the surface caused by the peening media's compressive force is substantially permanent, and thus should not return elastically to its original lattice microstructure.

The processing step 112 may also include grinding the multi-layer implant 200. For example, the zirconium alloy layer 215 can be ground using a fine polishing compound via a contacting-type grinding machine resulting in a substantially smooth, bright outer surface with a reduced number of scratches and visible grain boundary lines.

At step 114, the zirconium alloy layer 215 is oxidized to define an oxygen rich film, such as a zirconia layer 220 illustrated in FIG. 3. A zirconia surface demonstrates improved wear performance relative to cobalt chrome alloy and also provides a nickel-free alternative for patients with nickel sensitivities and/or allergies. The oxidizing step 114 may be accomplished either actively or passively, or a combination thereof. Zirconium-2.5 niobium, for example, oxidizes when exposed to air, with or without further intervention. However, the zirconium alloy layer 215 may additionally or alternatively be exposed to heat for a predetermined length of time to accelerate the oxidization process, which may produce a harder, smoother, and more uniform oxidized layer in reduced time as compared to passive oxidation. For example, the zirconium niobium MIM bodies can be heated to above 150 degrees Fahrenheit in an oxidative environment.

Further, the zirconia layer 220 provides surface characteristics, such as low friction coefficients, increased hardness, and resistance to wear and corrosion, that may equal or exceed those of wrought or forged oxidized zirconium-2.5 niobium medical implants. The zirconia layer 220 may define an implant-to-implant surface configured, adapted, and intended to interface with a complimentary implant surface.

At step 116, the multi-layered implant 200 may be post-processed. The post-processing step 116 of the multi-layered implant 200 may be performed in accordance with the specifications of desired implant. Surface finishing, such as mechanical grinding, and/or surface enhancement may be provided to the porous coating layer 210 and/or the zirconia layer 220 to result in a desired exterior characteristic.

FIGS. 2 and 3 show an exemplary multi-layered implant 200 in accordance with embodiments of the invention. FIG. 2 shows the multi-layered implant 200 implanted into a femur of a patient. For example, the multi-layered implant 200 may be a femoral knee implant. The femoral knee implant 200 may then be paired with a complimentary paired-knee member 300. Nevertheless, the multi-layered implant 200 is not limited to femoral knee implants and the multi-layered implant 200 may be shaped to form a variety of other implants including for example, any joint implant, such a uni-knee implant, a shoulder implant, an ankle implant, a spine implant, a disc implant, a hip implant, or the like. The paired-knee member 300 may be a multi-layered implant formed in accordance with any of the above-disclosed processes. Alternatively, the paired-knee member 300 may be formed of soft plastic.

FIG. 3 is a cross-sectional view of the multi-layered implant 200 depicted in FIG. 2. The multi-layered implant 200 may be formed in accordance with the method 100. The multi-layered implant 200 includes the MIM body 205, the porous coating layer 210, such as a porous titanium alloy layer 210. The porous coating layer 210 may cover an entirety of the implant-to-bone surface of the multi-layer implant 200, or may cover part of the implant-to-bone surface of the multi-layer implant 200, such as the portion directly contacting the bone. For example, the porous coating layer 210 illustrated in FIG. 3, covers a majority, but not all, of one side of the multi-layer implant 200. The porous coating layer 210 can have a thicknesses of 0.010-0.080 inches. The multi-layered implant 200 further includes the zirconium alloy layer 215 over-molded on the MIM body 205. The zirconium alloy layer 215 may cover an entirety of the implant-to-implant surface of the multi-layer implant 200, or may cover part of the implant-to-implant surface of the multi-layer implant 200, such as the portion directly contacting another implant. For example, the zirconium alloy layer 215 illustrated in FIG. 3, covers an entirety of one side of the multi-layer implant 200. The zirconium alloy layer 215 can have a thicknesses of 0.005-0.500 inches. The multi-layered implant 200 further includes a zirconia layer 220 formed on the zirconium alloy layer 215. The zirconia layer 220 may cover an entirety of the zirconium alloy layer 215, or may cover part of the zirconium alloy layer 215, such as the portion directly contacting another implant. For example, the zirconia layer 220 illustrated in FIG. 3, covers an entirety of the zirconium alloy layer 215. The zirconia layer 220 can have a thicknesses of 2-20 microns, and provide a hard, uniform, smooth, and dense surface.

Although various examples and embodiments of the multi-layered implant 200, and methods for manufacturing the multi-layered implant 200, have been disclosed, other implementations of the multi-layered implant 200 and methods for manufacturing the multi-layered implant 200 are contemplated. Many variations are contemplated for different applications and design considerations; however, for the sake of brevity, each and every contemplated variation is not individually described. All references to the multi-layered implant 200 or examples thereof are intended to reference the particular example of the present application and are not intended to be limiting. All methods described herein can be performed in any suitable order unless otherwise indicated herein. 

What is claimed is:
 1. A multi-layered implant, comprising: a Metal Injection Molded body comprising a titanium alloy; a porous coating layer on a first surface of the Metal Injection Molded body; and a zirconium alloy layer on a second surface of the Metal Injection Molded body, the first surface and the second surface being on opposite sides of the Metal Injection Molded body.
 2. The multi-layered implant of claim 1, wherein the porous coating layer comprises a titanium-based porous coating.
 3. The multi-layered implant of claim 1, further comprising a zirconia layer over the zirconium alloy layer.
 4. The multi-layered implant of claim 1, wherein the zirconium alloy layer comprises a zirconium-niobium alloy.
 5. The multi-layered implant of claim 1, wherein the multi-layered implant is a knee implant, a shoulder implant, an ankle implant, a spine implant, a disc implant, or a hip implant.
 6. A knee implant, comprising: a titanium alloy substrate; a porous coating layer on a first surface of the titanium alloy substrate; a zirconium alloy layer on a second surface of the titanium alloy substrate, the first surface and the second surface being on opposite sides of the titanium alloy substrate; and a zirconia layer over the zirconium alloy layer.
 7. The knee implant of claim 6, wherein the porous coating layer comprises titanium-based porous coating.
 8. The knee implant of claim 6, wherein the zirconium alloy layer comprises a zirconium-niobium alloy.
 9. A method of manufacturing a multi-layered implant, the method comprising: providing a Metal Injection Molded body comprising a titanium alloy; applying a porous coating on a first surface of the Metal Injection Molded body to form a porous coating layer, and a zirconium alloy on a second surface of the Metal Injection Molded body to form a zirconium alloy layer, the first surface and the second surface being on opposite sides of the Metal Injection Molded body; and oxidizing the zirconium alloy layer to form a zirconia layer over the zirconium alloy layer.
 10. The method of claim 9, wherein providing the Metal Injection Molded body comprises receiving the Metal Injection Molded body.
 11. The method of claim 9, wherein providing the Metal Injection Molded body comprises molding the Metal Injection Molded body.
 12. The method of claim 9, wherein applying the zirconium alloy on the second surface of the Metal Injection Molded body comprises over-molding the zirconium alloy on the second surface of the Metal Injection Molded body to form the zirconium alloy layer.
 13. The method of claim 9, further comprising: sintering the Metal Injection Molded body; and hot isostatic pressing the Metal Injection Molded body.
 14. The method of claim 13, wherein sintering the Metal Injection Molded body comprises: sintering the porous coating on the first surface of the Metal Injection Molded body; and sintering the zirconium alloy on the second surface of the Metal Injection Molded body.
 15. The method of claim 9, further comprising polishing the zirconium alloy layer.
 16. The method of claim 15, wherein polishing the zirconium alloy layer comprises applying an abrasive finishing process to the zirconium alloy layer.
 17. The method of claim 9, further comprising heat treating the zirconium alloy layer.
 18. The method of claim 9, wherein oxidizing the zirconium alloy layer comprises heating the zirconium alloy layer in an oxidative environment to form the zirconia layer.
 19. The method of claim 9, further comprising mechanically finishing the zirconia layer.
 20. The method of claim 9, wherein the zirconium alloy comprises a zirconium-niobium alloy. 